Combustion apparatuses such as boilers or water heaters are devices in which heating water in a sealing container is heated by a heat source to heat a desired area or supply hot water. The combustion apparatus is constituted by a burner burning mixed-gas in which a gas is mixed with air and a heat exchanger for transmitting combustion heat of a combustion gas to the heating water or direct water.
FIG. 1 is a schematic view of a combustion apparatus according to a related art. A condensing boiler is described as an example. The combustion apparatus 10 according to the related art includes a blower 11 suctioning external air to supply the air needed for combustion, a burner 12 for burning mixed-gas in which the air supplied through the blower 11 is mixed with a gas, a combustion chamber in which the mixed-gas is burnt, a sensible heat heat-exchanger 14 that absorbs combustion sensible heat generated from the combustion chamber 13, a latent heat heat-exchanger 15 that absorbs latent heat of vapor contained in a combustion product that is heat-exchanged in the sensible heat heat-exchanger 14, and a duct 16 through which the combustion product passing through the latent heat heat-exchanger 15 is discharged.
The heating water heated while passing through the sensible heat heat-exchanger 14 and the latent heat heat-exchanger 15 may be transferred to a heating consumption place through a supply tube 17 connected to one side of the sensible heat heat-exchanger 14 to transfer heat energy and then return to a return tube 18 connected to one side of the latent heat heat-exchanger 15. Then, the heating water returning to the return tube 18 may be introduced into the latent heat heat-exchanger 15 to condense vapor contained in a combustion product passing through the sensible heat heat-exchanger 14 to recover the latent heat.
Since the above-described combustion apparatus 10 according to the related art has a structure in which the external air is directly introduced into the blower 11 and supplied to the burner 12, when the external air supplied to the blower 11 has a relatively low temperature, a combustion load has to be increased to increase a temperature of the combustion sensible heat generated when the mixed-gas is burnt in the burner 12 up to a temperature range that is required to heat the heating water. Thus, the combustion apparatus is reduced in combustion efficiency, and also as fuel consumption increases, an emission amount of carbon dioxide (CO2) increases.
Also, in the combustion apparatus 10 according to related art, since the heat-exchanged combustion gas is discharged as it is through the duct 16 into the atmosphere, an emission amount of nitrogen oxide (NOx) increases due to a high temperature of the exhaust gas and a high flame temperature of the combustion gas to cause environmental contamination.